The y-coordinate is a value that represents a point's vertical position on a two-dimensional graph or coordinate plane. In the Cartesian coordinate system, each point is defined by an ordered pair of numbers, usually written as x, y. The y-coordinate indicates how far up or down the point is located from the horizontal axis, known as the x-axis. When the y-coordinate is positive, the point is above the x-axis, while a negative y-coordinate means the point is below it. For example, in the point 3, 4, the y-coordinate is 4, indicating it is four units above the x-axis. Understanding y-coordinates is essential for graphing functions and analyzing data.